Search

The structural vibration and the sound radiation induced by the flow over a cavity on a hydrofoil are investigated experimentally and numerically. The large eddy simulation (LES) is adopted to calculate the flow field and the pressure fluctuation characteristics. A coupled finite element method/boundary element method approach is used to analyze the hydrofoil vibration and the structure-borne noise. The flow noise is calculated using an acoustic analogy by considering the surface pressure fluctuations as the dipole sources. A hollow hydrofoil with an orifice supported by four cylinder rods is constructed for the experiments. Modal tests are performed to obtain the natural frequencies of the hydrofoil in air and water. The vibro-acoustic experiments are carried out in the water tunnel at various free stream velocities with the orifice open and closed. A pressure transducer is used to measure the pressure fluctuations behind the downstream edge of the orifice. The triaxial accelerometers mounted on the side walls are used to measure the vibrational response of the hydrofoil. Furthermore, a hydrophone located in a box, filled with water is used to measure the sound radiation. The structure-borne noise and the flow noise are identified by their frequency properties. Reasonable agreements are observed between the numerical predictions and the experimental measurements.

In-situ electrification lifting of transmission towers is a safe, reliable and economical construction method developed in recent years. In this paper the self-climbing mandrel transfer mechanism was described in detail and the live in-situ lifting of a 110kV dual-circuit iron tower was used as an example to describe in detail the lifting process and force analysis of the self-climbing bar in the in-situ live charging technology, which shows the reliability of climbing rod in the lifting process.

In order to study the vibration characteristics of flow-induced open cavity structures, the dynamic model of stiffened multi-plate is established. The first-order shear deformable plate theory and the Timoshenko beam theory are used to model the displacement fields of isotropic plates and stiffeners, respectively. A modified variational principle combined with a multi-segment partitioning procedure is employed to formulate the discretized equations of motion. The stiffeners are considered as discrete elements, and the energy contributions are included into the system energy functional by using the displacement compatibility conditions. The displacement and rotation components of each plate segment are expanded by a duplicate series of Chebyshev orthogonal polynomials of first kind. The convergence and accuracy of the present results for isotropic stiffened plates with different boundary conditions have been validated using comparisons with the published data and those obtained from the finite element analyses. Free vibration and dynamic responses of stiffened multi-plates with either longitudinal or orthogonally oriented stiffeners are discussed. The mathematical model and methodology presented in this paper may be used as an appropriate numerical tool in the analysis and design of stiffened multi-plate structures.

The vibration and stability of axially loaded sandwich cylindrical shells with the functionally graded (FG) core with and without shear stresses and rotary inertia resting Pasternak foundation are investigated. The dynamic stability is derived based on the first order shear deformation theory (FSDT) including shear stresses. The axial load and dimensionless fundamental frequency for FG sandwich shell with shear stresses and rotary inertia and resting on the Pasternak foundation. Finally, the influences of variations of FG core, elastic foundations, shear stresses and rotary inertia on the fundamental frequencies and critical axial loads are investigated.

The prediction of the flow-induced noise level is a key issue in the fluid–dynamic acoustics. In the hydroacoustics field, the complicated feedback induced by the flow past open cavities can amplify the convection instability in the shear layer which further leads to important noise radiations. The noise consists of intense narrowband and broadband components. In this paper, the level of the noise radiated by a subsonic cavity flow is calculated by using numerical flow computations based on the large eddy simulation (LES) and by solving the Ffowcs Williams-Hawkings equation. A series of three-dimensional open cavity models with overset grids and appropriate boundary conditions are developed for the hydroacoustic numerical computation. The self-sustained oscillation characteristics of the cavity flow are investigated, together with the mechanisms of the cavity noise generation. The distinguishing features of the flow-induced noise of the underwater structure cavities are studied with respect to the parameters of the cavity models, such as the free stream velocity, the dimensions of the cavity mouth, the angle of the cavity neck, the horizontal and vertical porous cavity models and the actual submarine open cavity model with an incoming flow attack angle. It is shown that it may be feasible to reduce the flow-induced noise by appropriate optimal parameters of the underwater structure cavities.

In this study, the behavior of vibration of sandwich cylindrical shells covered by functionally graded coatings and resting on the Pasternak elastic foundation considering combined influences of shear stresses and rotary inertia are examined. It is assumed that the effective material properties of functionally graded coatings changes exponentially in thickness direction. The modified Donnell type equations of motion of functionally graded and homogeneous sandwich cylindrical shells on the Pasternak elastic foundation are deduced using the first-order shear deformation theory. Basic equations are reduced to an algebraic equation of the sixth order and numerically solving this algebraic equation gives the dimensionless fundamental frequency. The expressions for the dimensionless fundamental frequencies of functionally graded and ceramic coated sandwich cylindrical shells with and without taking into account the effects of Pasternak elastic foundation and shear stresses obtained in a special case. Calculations, the influences of an elastic foundation, compositional profiles of coatings, shear stresses, rotary inertia, and sandwich shell geometry parameters on the nondimensional fundamental frequency are described. The results are verified by comparing the obtained values with those in the existing literature.

Based on the code LS-DYNA, the simulation strategy on the quasi-static crushing process of composite tubes is studied by conducting two series of comparison simulations: one is at different virtual loading speeds with the real material density and the other is with different virtual material densities at the given loading speed. The simulation results are summarized as three types, namely mode-varying type (MVT), unstable type (UT) and stable type (ST), depending on the change of the structural failure mode and the occurrence of the load-fluctuating stage in the load-displacement curve. Analysis has shown that the steady load possesses the stability, the peak load has the convergence zone, and the thresholds of energy ratio can be adopted to evaluate the simulation results. In the end, the simulation strategy is proposed to makes it possible to acquire the simulation results with a higher query precision at a lower computing cost.

Adhesive bonding is one of the effective ways to reduce the weight of structures. Researchers have done lots of numerical analysis and finite element analysis taking into account of the complex stress state in the bonded area, as well as the stress singularity occurs at the overlap edges with a view to efficiently predict the strength and rigidity of adhesively bonded joints. As they may suffer shock or impact loads in practice which leads to high strain rate in structures, analysis methods for adhesively bonded joints differ from that at quasi-static condition for two reasons: one is the mechanical properties of materials, including adhesives and substrates are different at high strain rates, the other is the additional consideration of elastic wave propagation in solid body. This article summaries several finite element analysis methods for adhesively bonded joints at high strain rate developed by domestic and foreign scholars and corresponding experimental standards for determining required parameters of each analytical method and raised some questions that need for further study.

As the worldwide demand for crude oil and gas increases and the oilfields age, the annual production of produced water is rising dramatically. Environmental restrictions on the disposal of this waste water have become more stringent in recent years with the result that disposal costs are also raising rapidly. This paper examines the various options for the treatment of this produced water prior to its disposal together with the possible consequences of getting it wrong, such as corrosion and scaling of process piping and equipment, together with fouling of the oilfield rock formation and disposal wells.

Vibration signal analysis is the main technique in machine condition monitoring or fault diagnosis, whereas in some cases vibration-based diagnosis is restrained because of its contact measurement. Acoustic-based diagnosis (ABD) with non-contact measurement has received little attention, although sound field may contain abundant information related to fault pattern. A new scheme of ABD for gearbox based on near-field acoustic holography (NAH) and spatial distribution features of sound field is presented in this paper. It focuses on applying distribution information of sound field to gearbox fault diagnosis. A two-stage industrial helical gearbox is experimentally studied in a semi-anechoic chamber and a lab workshop, respectively. Firstly, multi-class faults (mild pitting, moderate pitting, severe pitting and tooth breakage) are simulated, respectively. Secondly, sound fields and corresponding acoustic images in different gearbox running conditions are obtained by fast Fourier transform (FFT) based NAH. Thirdly, by introducing texture analysis to fault diagnosis, spatial distribution features are extracted from acoustic images for capturing fault patterns underlying the sound field. Finally, the features are fed into multi-class support vector machine for fault pattern identification. The feasibility and effectiveness of our proposed scheme is demonstrated on the good experimental results and the comparison with traditional ABD method. Even with strong noise interference, spatial distribution features of sound field can reliably reveal the fault patterns of gearbox, and thus the satisfactory accuracy can be obtained. The combination of histogram features and gray level gradient co-occurrence matrix features is suggested for good diagnosis accuracy and low time cost.

Adhesive-bonded composite integrated structures (ACIS) are widely used in civil and military aircrafts now. The failure laws of such structures should be studied obligatorily to design them reasonably. In a composite wing-box test debonding damage was found at the connection between the skin and the wall in mechanical-joint region while the load was added up to certain magnitude. However the shear stress of the adhesive layer in plane was not high. The real reason of the damage is that there is significant out-plane normal tensile stress at the local place. The main factors, which induced out-of-plane normal tensile stress, include out-of-plane force resulting from changing of force transfer path and sudden change stiffness. In this paper an integrated composite I-beam is investigated to expound the existing objectively of out-of-plane force, and analyze the relationships between out-of-plane force, sudden change stiffness and out-plane normal tensile stress or peeling stress. Research indicates that the out-of-plane force and debonding damage resulted from it should be highly valued for ACIS in mechanical-joint region.

Just like the steel bars, the connection of FRP bars is needed in engineering application. But most of the steel bars’ traditional connection ways are not suitable for FRP bars because of the differences of the material properties. With the engineering application standards’ appearing, it is becoming an urgent need that we should have one or some connection methods for FRP bars which can be selected and used by engineers. This paper presents a brief overview about the research progress of FRP bars’ connections, gives the definition and the design principles of FRP bars’ connection, emphatically introduces the research progress of coaxial connection of FRP bars, and discusses the off-axis connection ways. At last, we put forward some works that need to be further researched.

A severe disease was observed on sunflower (Helianthus annuus L.) in Ili, Xinjiang China, in 2005. The causal agent was isolated from infected tissues, and its pathogenicity confirmed. Pathogenicity tests showed that the fungus could infect sunflower, which developed the same symptoms under artificial inoculation conditions to those observed in the field. The fungus was identified based on morphological and cultural characteristics as Phoma macdonaldii Boerema. Identifications were confirmed by comparison of the 18S rDNA partial sequence, 28S rDNA partial sequence, and the internal transcribed spacer (ITS) regions 1 and 2, including 5.8S rDNA (ITS1‐5.8S-ITS2). This is the first report of black stem of sunflower caused by P. macdonaldii in China.

Economical and effective oily sludge pyrolysis residue was prepared, characterized with various techniques, and applied in the removal of COD in biologically treated oil-field wastewater. It was found that surface area of oily sludge pyrolysis residue was 223.62 m2 /g. The content of C and Al2O3 was 27.91% and 27.6%, respectively. Oily sludge pyrolysis residue contains carboxyl, hydroxyl, carbonyl and other oxygen-containing acid functional groups. When the adsorption equilibrium time of oily sludge pyrolysis residue was 90min, pH of solution was 4, the best COD adsorption capacity was 59.5 mg/g. Adsorption of oily sludge pyrolysis residue is determined by its structure and composition. The Al2O3 may play a flocculation and sedimentation role in COD removal, which has a synergistic effect on adsorption. The adsorption of COD from biologically treated oil-field wastewater by oily sludge pyrolysis residue follows Langmuir adsorption isotherm.

Glass fiber reinforced plastics (GFRP) rebars / bolts are more and more being applied in construction projects with its superior corrosion resistance. To improve the economical efficiency of their application it is very significant to develop the prestressed GFRP rebars/bolts structure system. Therefore it is very valuable to probe the stress relaxation properties of GFRP rebars/bolts. With an innovation ends anchoring method for stress relaxation specimens of GFRP rebars/bolts, the stress relaxation properties has been tested in this paper. Results show that the relaxation rate of GFRP rebars/bolts increases with the initial stress increasing and with test time prolonging. It is increasing more rapidly at the beginning stage and it becomes slow after 24 hours. The relaxation law of GFRP rebars/bolts is similar to the law of CFRP and AFRP rebars/bolts. The relation between the relaxation rate and the logarithm of test time in hour follows also better linear law. The relaxation rate of GFRP rebars/bolts is bigger than CFRP ones and smaller than AFRP ones. The mechanical properties do not change obviously after 120h relaxation test.

According to the water quality monitoring data for Bashang section of Jian-gang reservoir conveying water for South-North Water Transfer Project from 2006 to 2009, individual evaluation, overall merit and evaluations of flood season and non-flood season were employed for water environmental quality evaluation with visualize classification on the ground of water quality standard classification, the results indicated that the evaluation indexes of flood season were higher than that of non-flood season and overall merit were with class I, thus overall water quality was good enough for satisfying water quality requirements for supplying of South-North Water Transfer Project, the water quality of non-flood season was better than the flood season.